Instrumentation the Arm of a Robot Welding

PINHEIRO BECK, Joao Carlos¹, SILVA, Renato Molina² & SOUZA, Alexandre Reus Baroni³

¹ Av. Ipiranga, 6681 - predio 30/169 - CEP 90619-900 - Porto Alegre - RS - Brasil, PUCRS - Faculdade de Engenharia/Departamento de Engenharia Mecanica e Mecatronica, dem_feng@pucrs.br
² Av. Ipiranga, 6681 - predio 30/169 - CEP 90619-900 - Porto Alegre - RS - Brasil, PUCRS - Faculdade de Engenharia/Departamento de Engenharia Mecanica e Mecatronica, dem_feng@pucrs.br
³ Av. Ipiranga, 6681 - predio 30/169 - CEP 90619-900 - Porto Alegre - RS - Brasil, PUCRS - Faculdade de Engenharia/Departamento de Engenharia Mecanica e Mecatronica, dem_feng@pucrs.br

1 Introduction

The welding process are usual to make products and metals structures, planes and space vehicles, ships, train engines, railway vehicles and highway vehicles, bridges, buildings,... [Ferguson 1997].

Two points must be taken in consideration when analizing the welding technique:

• It's based on principles that were from the experience and it depends on a large number of parameter, what makes the technique very had to formulate mathematicaly.
• It depends almost fully on the man and its total checking is very dificult, what makes the process aa very hard to control one.

The automatization of the welded equipament fabrication's steps means that all, or almost the operations must be automated by mechanical sistems, eletromechanics or eletronics. The automation leves depend of the characteristics of each process and of the welding conditions [Lynehburg 1997]. The use of the arrangement to the automation has several consequences that must be examined, specialy when it's refered to:

• Weld's quality: in the automation, the control process variable its made by eletromechanics or eletronics dispositives; this way, increase the reproduction of one qualified weld, decreasing the human's mistakes ocorrence. This way reduces a minimum the presence of glows and, as well, the time to repair the components [Sorenti 1997].
• Level of production: in the case of automatized systems the time which he keeps him self productive is bigger, decreasing the costs of production, it's important that the systems has some susceptibility about the king of welding to be executed.
• Direct labour: the work of the manual welder it's not always executed in appropriated environment. In case of whealty places, or with hard acess, the automatized system can be replaced with gain.
• Investiment: the automatized systems envolves high level of advantage, being needed on analysis very minucious of the investiment and it's profit, before bracing the cause.

2 Development

The main objective of the work was to make a semi-automatic process of welding, using a robot that could grab the torch of welding and weld, through software commands, creating a interface based on contacts that could make this operation (CLP) with seccurity and certainly [Dally 1993].

Were used the following equipments and dispositives:

• Robot Scorbot ER V-PLUS of Eshed Robotec
• Welding system of Lincoln Electric

Dispositives of integration:

• Two solid state relay, with input of 3 to 32VDC and output of 24 to 330VAC with 10A.
• Siemens contactor
• Diodos

From the beginning we had to build na adapter so it wasn't necessary to dismount the robot's own claw, making easier the process. As the robot stands 1kg tops in the claw, was needed or part for adaptation that was made of a resistent material of nylon, with a relative complex geometry, since it should be something with precises dimensions, easy to adapt in the robot's claw and at the some time firm.

So the project of the adapter became completed was needed to be made two and half circles with thread of 8mm, and the use of four adjusting lock nuts with lock washers to fix the torch wich length of the niplle is 8mm.

Another project developed was the criation of some kind of "pedestal", so the robot could release the torch/adapter and stay free to execute other operations if necessary. In the specific case of the project the objective was to use the robot to grab the raw material and them be able to move the final product. The material used to make the pedestal was iron carbon steel SAE 1020, with retangular base and toscrew on the welding table.

The procedures were:

• First procedure:

  Conection of the generation and active the welding torch.

  Make that, by software, could be possible to conect the generator and active the torch in the exact time that it is necessary. For that was used a relay and a contactor to conect the generator and another relay to activate the torch. As the model of controler used has a 16 input's capacity, only two ways out were used [Nise 1992].

• Second procedure

  Execute movements of the claw with the torch.

  Was created a program using a robot's language (ACL), that make possible the entrance and outlet of the claw with the torch, and that could be free when necessary to make others assignements.

  In this program the robot execute a welding simulation, so he grabs the torch of the pedestal, take it to a neutral (one point above) and executes two points of welding, onde which side of the joint then he executes one pitch of root in the chamfered joint (0,7mm), comes back to the neutral position and puts back to the torch over the pedestal. The program makes a "looping" and only stops if have a command to cancel.

• Third procedure:

  Execute points of weld MIG through a software.

  The main problem to the complete automation of this process was the kind of generator used, that couldn't "trade informations" with the controler. To each kind of welding it was needed to manually regulate parameter of weld. In the other hand, one of the good things is that the generator had a semiautomatic characteristic, because when is was regulated the electric current that variated between 120A and 150A, automaticaly, stayed regulated the gas out let (C21) and the speed of advance of the welding wire making easier the final operation.

• Fourth procedure:

  There were difficulties to adjust this level of welding because of several reasons. The main one was the vibration. In robotics we know, there are two things that don't ride together: precision and load. Has it was written before, the robot was working in the limit of it's load, there was too much vibrations, so it makes the bow unstable leaving the string disorganized. Depending on the movement executed, the monocable with the torch became more and more havy, ore less havy, also making the trajectory unconstant, putting errors on the system. Another reason was the kind of gas used that wasn't the most qualified, because it usually make the opening of the bow not constant. To try to apart the problem of the monocable was put a staff that helped to keep it high and absorve the vibrations, what improved a lot the final result.

3 Results

With the materials and the adapted procedures, those were the final results:

1. An automatized process was reached, on low const and precise to the execution of the welded point.
2. With the language, materials and used dispositives, was developed a process very flexible, wich the robot used can be applyed to execute other procedures of manufactory with preciseness.
3. According to the king of gas used and the unapplience of the source of tension to the openning of the arch, strings of weld was made with exactness and uniformity can be improved.

References

FERGUSON JR., C. R. & KLINE, M.D. 1997. In Soldagem adaptável para estaleiros. Industrial Robot. Number 5. Volume 24.

LYNEHBURG. 1996. Virginia, USA

SORENTI, PETER. 1997. In Robo de soldagem eficiente para estaleiros e simulacao de validade virtual. Industrial Robot. Number 1. Volume 24.

DALLY, J. W. et alli. 1993. In Instrumentation for engineering Measurements, John Willey & Sons.

NISE, NORMAN. 1992. In Control Systems Engineering, the Benjamin Cummings.